Positioning of submarine tubes



Sept. 20, 1966 DELARUELLE ETAL 3,273,346

POSITIONING OF SUBMARINE TUBES Filed Dec. 18, 1961 2 Sheets-Sheet 1FIG.2

POSITIONI NG OF SUBMARINE TUBES Filed Dec. 18, 1961 2 Sheets-Sheet 2FIG.4

M40005: fizzmwa 4 5 Zia/v CamrnoA/r/A/ g w #JM United States PatentOfiice 3,273,346 Patented Sept. 20, 1966 3,273,346 POSITIONING FSUBMARINE TUBES Jacques Delaruelle, Paris, and Lon Constantin,Villecresnes, France, assignors to Electricite de France (ServiceNational), Paris, France, a French National Service and Gaz de France(Service National), Paris,

France, a French National Service Filed Dec. 18, 1961, Ser. No. 160,191Claims priority, application France, Mar. 21, 1961,

1 Claim. (31. 6172.3)

This invention relates to the positioning of submarine tubes orpipelines and particularly to positioning such tubes at great depthsemploying the technique of attaching additional horizontal sections ofpipeline to a section of the already laid cable or pipeline.

In the specification of co-pending patent application Ser. No. 99,148,now abandoned, a method of positioning a submarine tube so as to enablefresh sections of the tube to be attached to a previously laid sectionof the tube is described and claimed. That method comprises the steps ofapplying to the end of the section of the tube already laid horizontaland vertical forces by means of immersed floats so as to cause the tubeto assume a substantially S-shape curvature with the upper end thereofsubstantially horizontal and defining a downwardlydirected concavity,successively releasing the vertical forces from the tube in a region ofpredetermined depth where the curvature of the tube passes through apoint of inflection, and successively applying vertical forces to thetube in the region where the curvature of the tube is substantiallyhorizontal.

In this method, the curvatureof the section of tube already laid isproduced by the combined action of a horizontal traction applied to theend of the tube already positioned and of a number of vertical forcesappropriately distributed along the upper portion of the said tube andproduced by means of a series of lightening floats.

The performance of this method necessitates either the unhooking of atleast some of the lightening floats as positioning progresses beyond aregion of predetermined depth, and the rehooking of the same onto thefreshly added sections, or the use of floats constructed progressivelyto lose their buoyancy which diminishes and loses its lifting effect ata certain depth.

The present invention is concerned with an improvement of the aforesaidmethods and makes it possible to avoid, in the former case, the periodichooking and unhooking of the floats and consequently to economize thefleet of boats necessary for laying the tube, and, in the latter case,the loss of the variable-buoyancy floats or the difiicult problem oftheir recovery.

According to one aspect of the present invention there is provided amethod of positioning a submarine tube so as to enable fresh sections ofthe tube to be attached to a section of the tube already laid, whereinthere are applied to the end of the section of the tube already laidhorizontal and vertical forces to cause the tube to assume a substantially S-shaped curvature with the upper end thereof substantiallyhorizontal and defining a downwardlydirected concavity, and wherein thevertical forces are applied to the tube through the intermediary of aflexible guide connected to a rigging craft, positioning being effectedby imparting a horizontal translational movement to the guide and bysliding the tube relative to the guide. In other words, the upperportion of the tube is carried by the aid of a guide which is itselfcarried by floats or other lightening means distributed appropriatelyalong its length so as to impart the desired curvature to it.

By virtue of this arrangement, positioning may be performed by simplysliding the tube through the guide at a speed equal to the speed ofhorizontal translation of the guide and of the tube between the bot-tomand the surface. In this manner at least a part of the lightening forcerequired for positioning the tube the attainment of which forcegenerally represents a large proportion of the cost of the tube, is notexerted directly on the latter but on the guide. Each new tube elementto be positioned is butt-jointed to the extremity of the previouselement which has arrived close to the entrance of the guide, and is inturn introduced into the latter. The said elements may be sections ofgreat length brought up either in the holds of ships or by flotation.They may likewise be comparatively short sections assembled by screwingor welding on board a factory ship which performs the positioning andcarries the entrance of the guide.

This invention also relates to a device for performing the above method,such device including the aforesaid guide.

This guide is intended to guide and carry the submarine tube between itsupper extremity or extremity of entry located close to the surface ofthe sea Where the tube is horizontal, and its lower extremity orextremity of exit which is close to the point of inflection of the tube,and the guide will necessarily have a comparatively great length; sincesubmarine tubes do not usually permit radii of curvature less than sometens of metres, the length of the guide will be from some tens to somehundreds of metres.

This comparatively great length makes it necessary that the guide shouldbe deformable so as to be able to resist the constraints to which it issubjected on the part of the tube, of its lightening means, and ofmarine currents. Thus it is necessary for the guide to have anarticulated or flexible structure, not merely in the vertical plane inwhich the desired curvature is in principle located, but also in thehorizontal plane. Indeed, whereas in the case of positioning in theabsence of transverse currents the S-shaped curve of the tube iscontained in a vertical plane, in the general case where marine currentsare present and have a component of motion perpendicular to thealignment of the tube, the upper portion of the tube will describe askew curve in the region of action of the currents.

The guide must be as light as possible, so that its own lightening meansintended to support it in the water shall not be excessively voluminous,as this would render it expensive and would likewise confer thedisadvantage of presenting too great a grip or purchase for marinecurrents.

As the tube is acted upon by its own weight, which may be considerable,it is necessary to provide a braking system capable of resisting therelative movement of the tube with respect to the guide with a force atleast equal to the said action.

Accordingly, another aspect of the present invention provides a devicefor positioning a submarine tube so as to enable fresh sections of thetube to be attached .to a section of the tube already laid, wherein thedevice comprises an elongated guide which is flexible both in itslongitudinal direction and transverse thereto, the guide being capableof supporting the tube to be positioned between an upper extremity ofentry adapted to be connected to a rigging ship, and a lower extremityof exit, and wherein means is provided for exerting a vertical force onthe guide, when immersed, to impart thereto a curvature defining adownward concavity between the two said extremities, the upper of whichlies substantially horizontal, there also being provided a brakingdevice adapted to oppose the relative movements of the tube by a forceadjustable at will.

The braking device is desirably arranged at the entrance of the guide,and this arrangement provides the advantage in practice, that, becauseaswill be seen hereinafterit is by adjusting the braking action that thespeed of positioning is regulated and, more particularly, that stoppageof the said positioning is obtained.

The guide may take various forms, such as for example, a chain of rollertype cradles, which would be capable of supporting and guiding the tubeand of presenting the required double flexibility by virtue of a seriesof appropriate articulations, to which the lightening or additionallightening floats of the guide might be hooked. However, the guide ispreferably a cylindrical guide tube extending with a substantiallyuniform internal cross-seetion adapted to permit sliding of the tubewith suflicient play between two flared end nozzles.

Such a tubular structure presents surprising advantages, since theassembly of the tubular structure with the submarine tube in itsinterior behavesfrom the mechanical standpoint-like a flexible ropestretched in a flexible sheath, and the longitudinal compression of thesheath at each point does not lead to buckling thereof, by reason of thecorresponding tension of the tube at that point. The guide sheath may,advantageously be made of steel having a thickness of only a fewmillimetres in order to resist simple compression. Since its internaldiameter is close to the external diameter of the tube, it is protectedby the tube itself against any tendency to undulate. The constructionbecomes especially simple and economical in the case where the sheath isconstructed of sections of 10-15 metres in length as it is then possibleto hook floats onto sleeves connecting the said sections. It is easy toprovide a primary lightening means in the form of bundles attached tothe periphery of each section so as to provide the guide itselfimmediately with a low weight in water and thus to reduce the buoyantcapacity required for the floats. The flexibility imparted to the tubeby its slight thickness is amply suflicient to provide the guide withthe double flexibility which is required simultaneously in the verticalplane and in the transverse direction. The flared end nozzles facilitatethe entry and the exit of the tube and avoid the risk of damage to theanti-corrosive cladding with which the latter is generally fitted.

Such a tubular guide is readily transported between two positioningoperations by towing it between different 10- cations in the same manneras a section of the tube. For this purpose, it is suflicient for theprimary lightening means secured directly to the external face of theguide to provide the latter with a low weight in water-for example, 2kg./rn.the balance of the lightening means being constituted by floatsattached to the guide by means of guy-ropes of sufficient length tolower the guide to a position where it is unaffected by any surfaceswell.

In order to enable the invention to be more readily understood,reference will now be made to the accompanying drawings, whichillustrate diagrammatically and by way of example some embodimentsthereof, and in which:

FIGURE 1 is a diagrammatic elevation of a method of laying andpositioning a submarine tube using a guide having lightening meansdistributed uniformly along it,

FIGURE 2 is an enlarged cross-section taken along the line IIII inFIGURE 1,

FIGURE 3 is a view similar to FIGURE 1 showing another method of layingand positioning a submarine tube, employing variable lightening meansalong the guide, and

FIGURE 4 is an enlarged cross-section taken along the line IVIV inFIGURE 3.

Referring now to FIGURES 1 and 2, there is shown the positioning of asubmarine tube 10 which is being laid at a depth H. That portion of thetube 10 which is not yet in contact with the bottom has its extremitysubjected to a horizontal tractive force in the direction of the arrow Aand produced by one or a plurality of tugboats, not shown in thedrawings. A tubular guide 11 extends from a flared nozzle 12 forming itsupper extremity or extremity of entry to a flared nozzle 13 forming itslower extremity or extremity of exit, the extremity 12 being immersed inthis case to a depth of a few metres and attached by means of cables 14to a positioning ship 15. Instead of attaching the guide to the ship, itis also possible effectively to render the guide integral with the shipby anchoring it in the ship, as will hereinafter be described withreference to FIGURE 3. The tubular body 11 of the guide is composed ofsections of a steel pipe having an internal diameter slightly greaterthan the external diameter of the tube (or more precisely, of connectingsleeves of the latter) in such a manner that the tube is able to slidethrough the body 11 of the guide. As shown in FIGURE 2, each section ofthe tubular body 11 is covered externally with a bundle of rods 16 ofcellular material such as expanded polystyrene, constituting a primarylightening means, and a series of floats 17 are hooked through theintermediary of brackets 18a to the connecting sleeves 18 of adjacentsections of the guide by means of guy-ropes 19, which are, for example,some 15 metres in length. The connecting sleeves 18 will advantageouslybe of the screwthreaded type, which enables the guide to be shortened orlengthened more readily whenever necessary.

A device for braking the tube is constituted by a toroidal hollow body20 of flexible material disposed round the tube adjacent the entrynozzle 12, and connected by a flexible pipe 21 to a source ofpressurized fluid (not shown in detail) arranged on board the ship 15,means being provided for regulating the pressure of the said fluid asrequired between certain limits. Such braking devices are disclosed ingreater detail in US. Patent No. 2,775,- 86 9, Jan. 21, 1957, and alsoin French Patent No. 1,081,- 361, Dec. 20, 1954, and its Addition No.66,721, Aug. 19, 1957, and in French Patent No. 1,132,160, Mar. 6, 1957.Reference is made to these prior patents so as to avoid the inclusion ofunnecessary disclosure of known structure in the present application.

As may be seen in FIGURE 1, the guide 11 supports the tube 10 and guidesthe same, between the entry nozzle 12 located close to the surface andthe exist nozzle 13 located at a certain depth h along a curve ofdownward concavity between a substantially horizontal point of departureat the entry 12 and a point of inflection I lo,- cated in the vicinityof the exit 13.

The immersion to a depth of some metres of the upper extremity of theguide, as illustrated in FIGURE 1, presents the advantage of shelteringthe guide from the effects of any surface swell.

The first element of the tube to be positioned with the guide is placedin the tubular guide structure at the shore workshop where the elementsare prepared, and the Whole is launched and towed to the point ofcommencement of positioning or of connection of the said element to aportion of tube already positi0ned-possibly by other methods. The firstoperation therefore will be to butt-joint the rear extremity of thefirst element carried by the guidestill at the surfaceto the terminalportion of the tube already positioned. The said terminal portion may bemaintained provisionally in the S-shaped position requiredto that end bymeansfor exampleof appropriate floats according to any one of thetechniques we have described elsewhere. The S-shaped configuration ofthe tube and guide will be established as the terminal portion of thetube already positioned is allowed to descend towards the bottom,involving in the said movement the first element carried by the guide.The chosen configuration having been effected, regulation of the speedof positioning is obtained from then onwards by means of the pneumaticor hydraulic brake 20, in proportion to the depth and desired speed ofpositioning. The new tube elements are brought up to the site from theshore workshop by towing, for example, and are equipped for that purposewith appropriate lightening means, the elements being freed from thesaid lightening means shortly prior to their arrival at the entrance tothe guide.

The shape of the guide may be the subject of a continuous check, bothduring positioning and during stoppage, and to this end a certain numberof-for example, manometricappliances giving the depth at thecorresponding points, and inclination indicators, if desired, may bedistributed along the guide. appliances can readily be transmitted tothe surface by means of suitably protected signalling cables attachedalong the guide. Since the said arrangements involve only well-known andtried techniques, it is not deemed necessary to show them in detail inthe accompanying drawings.

The guide such as described presents to the currents a grip or purchaselittle greater than that of the tube itself, so that its presence doesnot substantially increase the difiiculties of positioning across thecurrent. Its flexibility also enables it to assume easily the form of askew curve in the region of action of a current which is oblique withreference to the positioning direction.

If bad weather should make it impossible to continue positioningoperations, the assembly of tube and guide is completely immersed andlaid on the sea bed, so that it is sheltered from marine currents andfrom the swell. In order to facilitate the immersion, it is advantageousto effect a part of the lightening of the guide by means of floats whichare adapted to lose their bouyancy progressively with increasingdepth-for example, of compressible floats or of floats adapted to allowwater to penetrate when the external pressure exceeds a certain value.Such floats are described and claimed in the earlier-filed applicationof one of the present inventors, which matured to U.S. Patent No.3,114,920, Dec. 24, 1963. Reference is made to this patent in order toavoid the unnecessary disclosure of known structure in the presentapplication.

To effect immersion of the assembly to the sea bed, it is sufiicient toseal the tube element which is being positioned and to secure itsextremity to the extremity of the guide, to release the latter from thepositioning boat whilst disconnecting the pipe 21, to ballast it with adeadweight, and to exert on the assembly a fairly strong tractive force(for example, of the order of twice the normal positioning tractionforce A) by the aid of the cable or rope 14, for example. The effect ofthis tractive force is first to straighten slightly the S-shaped curveof the still unpositioned portion of the assembly of the tube and guide.The steel cable or rope .14 is then unwound, enabling the deadweight todrag the extremity 12 towards the bottom, and when the guide 11 hasarrived on the bottom, the steel rope is made fast to a buoy.

The buoy enables the tube to be marked, and to be returned to thesurface when weather permits positioning operations to be resumed.

In order to return the assembly to the surface it is merely necessary toraise the rope 14 in order to bring the extremity 12 of the guide up tothe surface. The use of the compressible floats referred to hereinabove,which regain their buoyancy above a certain depth, facilitates there-establishment of the S-shaped curve and the continuation of thepositioning operation.

When determining the lightening means to be disposed on the guide, theconditions of equilibrium when positioning is stopped must be taken intoaccount. During laying, the horizontal translation of the S-shaped curveformed by the tube and the guide generates hydrodynamic forces, thehorizontal components of which oppose the movement, but the verticalcomponents of which are directed upwards and are added to the liftingforce of the floats on the guide.

It can be shown that the general condition of equilibrium at rest of thetube and guide assembly between the bottom and the surface is expressedby:

rbf mmh (1) The indications of the said where p is the apparent weightof the tube in kilograms/meter,

H, the positioning depth in meters,

1 (h), the lifting force in kilograms per metre at a point of depth h(in meters) of the guide, and

h, the depth in meters of the lowest point of the guide located in thevicinity of the point of inflection I of the S-shaped curve.

The lightening means of the guide must therefore be constructed in suchmanner that the said relation is satisfied. It is also necessary for theradius of curvature in the vicinity of the surface in the leastfavourable casei.e. during stoppageto be greater than the minimum valuedictated by the mechanical strength of the tube and of the guide.

Where A designates the horizontal traction force in kilograms exerted atthe surface on the tube and guide assembly, and f(0) the buoyancy inkilograms/meter of the guide at the surface, it can be shown that theradius of curavture R, in meters, of the upper portion of the S-shapedcurve is given, if the rigidity of the tube and of the guide areneglected, by the formula:

It should also be noted that the rigidity always has a favourable effectupon the behaviour of the tube, but that its effect upon the shape ofthe S-shaped curve is generally negligible.

Taking these fundamental observations into account, various manners oflightening the guide are contemplated according to the presentinvention.

In the construction illustrated in FIGURE 1, the lightening means havebeen considered as uniformly distributed along the guide, and this isthe simplest arrangement.

It is easy to demonstrate that the guide in this case assumessubstantially the form of a catenary (except for the rigidity). If theadopted uni-form value of the lightening provided is designated by(corresponding to fo of Equation 2), the condition of equilibrium 1gives as the depth of the lowest point of the guide:

Taking f=2p, the point of inflection I is seen to be located at one halfthe depth, and the S-shaped curve is in that case constituted by twoidentical catenaries which have vertical axes, and which are tangentialrespectively to the bottom and to the surface, the catenaries beingconnected together at the point of inflection.

The said arrangement-the simplest-presents the drawback that itnecessitates a relatively great length for the guide, which increasesits cost and the cost of the lightening means. It is advisable to bringthe point of inflection I as close as possible to the surface byincreasing the buoyancy involving the necessity of simultaneouslyincreasing the horizontal tractive force A so as not to go below thedictated minimum radius of curvature.

A practical example of the application of this manner of uniformlightening will be given hereinafter:

Apparent weight of the tube p 10 kg. per metre. Positioning depth H 2500metres. Permissible radius of curvature R metres. Permissible tractiveforce A 4000 kg.

Under the above conditions, the depth h; of the point of inflection islocated at 500 m., and the length of the guide is approximately 600 m.

The buoyancy of the guide will have to be 50 kg. per metre (i.e., fivetimes the apparent weight of the tube) and the lightening means to beprovided in the guide will be equal to this value plus the apparentweight in water of the guide itself.

Since the tube when fitted with its covering has an external diameter-inthe particular case under consider- -ationof 270 mm., the guide will beconstituted by a steel-pipe of 300 mm. internal diameter and of aquality which will enable it to tolerate the radius of curvature of 100in. under a longitudinal compressive force equal to the maximum brakingforce-i.e., pH=25 tons.

Under these conditions, the guide should be mm. thick, as the maximumfatigue rate of the metal under these conditions is 40 kg./mm. in thecompressed state.

Since the weight in water of the guide thus constituted is 32 kg./-m.,the total lightening to be provided will therefore be 82 kg./m.

The primary lightening produced by the bundle 16 of rods of expandedpolystyrene (density 0.6) is 30 kg./m. and the secondary lightening of52 kg./m. is constituted by floats 17 having a buoyancy of 1600 kg.hooked at every 30 metres by guy-ropes metres in length.

The length of the guide is of course provided for the maximumpositioning depth to be contemplated. Where the depth is less than thismaximum, only one portion of the guide is immersed at depth, the otherremaining in the vicinity of the surface, so that the buoyancy of theguide shall correspond to the weight of tube in course of beingpositioned; this variation of the immersed length of the guide, andtherefore in the depth 11 of the point of inflection, is renderedpossible by the combined action of the horizontal traction force A andof the operation of the brake. Of course, this adjustment of the brakebecomes impossible above a certain limiting depth, and it is thennecessary either to exert the traction force A on the guide itself, orelse to shorten the guide, for example when butt-jointing a new section.

Instead of the uniform lightening considered hereinabove, it is likewisepossible to contemplate a variable system of lightening (FIGURE 3), andpreferably a form of lightening which increases with depth. It can beshown that if an increasing lightening f(s) kilograms/meter, is

disposed along the guide and has the value:

R cos where R is constant and s the distance in meters of the point inquestion from the origin S of the guide at the surface, the curve formedby the guide will be a circular arc of radius R, tangential to thesurface at S.

It is not usually possible to retain this law of distribution as far asthe point of inflection I, because the lightening (s) would then have toattain excessively high values, which are difficult to realise inpractice.

As from a specific' point M, it is thus necessary, for example, toretain a lightening of constant value kilo- .grams/ meter, and the curveis then continued beyond the said point M by a catenary arc.

It is possible to show by calculation that this manner of lighteningresults in a much smaller length and depth for the guide than in thecase of a uniformly distributed lightening, whilst simultaneously thetractive force A to be exerted at the surface may be relatively slight,and .now limited only by the curvature at the bottom.

(0)=10 kg./m. at the surface and a maximum f =250 kg./m. over a lengthof approximately 80 m. in the lower 1 portion.

To this variable lightening there will of course be added a uniformlightening of 42 kg./ m. corresponding to the 'weight in water of theguide and of the tube, also a lightening element to compensate for theweight of the floats themselves.

Referring now to FIGURES 3 and 4, which illustrate an example of such aconstruction, the reference symbols already used in FIGURES 1 and 2 arerepeated, accompanied by the index X to designate corresponding orequivalent elements.

It will be seen that the floats 17X are again attached to the guide 11Xthrough the intermediary of guy-ropes 19X and of brackets 18aX fastenedto the connecting sleeves. The above variable supplementary lighteningis composed of pipes 25 of increasing cross-section extending from theupper extremity of the guide, the pipes 25 being fastened end to endalong the guide and communicating with one another. The pipes 25 areopen at their lower extremity 27, and hence communicate with the sea,whereas at their upper extremity 28 they are placed in communication bya flexible pipe with a source of compressed air (not shown) carried bythe ship 15X.

In this manner, supplementary adjustment of the additional lightening iseffected in proportion to the positioning depth. This supplementaryadjustment is necessary here, because it is no longer possible to causea variable initial portion of the guide to rise to the surface when thepositioning depth becomes smaller; the result of this would be todiminish the radii of curvature at all points.

The device described enables the length of lightening of the guide nearits lower extremity towards the point of inflection Iand hence the depthof that pOint--t0 be regulated. It will be seen, in fact, that thesupplementary lightening produced by the pipes 25 exists only above thelevel at which the water rises in their interior. Now, this level isdetermined by the air pressure of the compressed air source from theship. If the guide has a tendency to rise to the surface, the pressureis reduced so as to make its lower portion heavier, but if on thecontrary it tends to sink, the pressure of the compressed air source isincreased until equilibrium is achieved.

In the case of the example considered, the said variable lightening isconstituted by the two pipes 25 which are arranged on each side of theguide, and the diameters will vary between mm. at the upper extremityand 400 mm. towards the lower extremity.

The conditions of braking and of longitudinal compression of the guideremain unchanged.

In the case of the construction illustrated in FIGURE 3, the upperextremity 12X of the guide is taken on board the ship 15X, where thebutt-jointing of the successive tube elements may be effected. In thiscase, the extremity of the guide is anchored and made integral with thecraft, and braking of the tube may be effected by any known systemforexample, the ships brake or a caterpillar of the type indicated at20Xwhich is arranged on the deck of the ship and in which the tube isengaged.

In the event of bad weather, in this case as with the previous example,steps will be taken to immerse the tube and guide assembly and lay it onthe sea bed after disengaging the extremity 12X from the ship 15X. Thisoperation is facilitated in the present case by the variable lighteningconstituted by the pipes 25. It is in fact sufiicient to bleed the aircompletely from the pipes in order to immerse the assembly. Uponsubsequent raising, the pipes are repressurised when the extremityreaches the surface.

It should also be noted that during the course of operation the slidingmovement of the tube in the guide naturally depends upon the friction.However, the total effect of friction on the tube in the guide isusually very much lower than the braking force requiring to be exertedbetween the tube and the guide. There is therefore a favourablediminution of the braking required. In the course of the studies onconstruction shown in FIGURES 1 and 2, it was possible to estimate themagnitude of the braking force by distinguishing between the followingthree terms:

(1) Friction on that portion of the guide located betWWIt $11G point ofinflection I and the surface;

(2) Friction on that portion of the guide which possibly remains in thevicinity of the surface (in the case of uniform lightening with reducedpositioning depth);

(3) Friction resulting from undulations produced by the localised forcesof the floats.

In the example considered above, the calculations performed yield atotal friction force of approximately seven to eight tons, taking aco-eflicient of friction at rest of 0.2 and a distance of 30 metresbetween localised floats. The braking force exerted at rest is thereforereduced, by virtue of the friction, to only 1718 tons for a depth of2500 metres.

During positioning, the reduction in the frictional resistance of thetube against the guide due to the lowering of the coeflicient offriction is more or less compensated, as regards the braking force to beexerted, by the hydrodynamic forces which-as stated hereinabove-producean additional lightening of the tube, which is subtracted from the totalweight pH to be compensated.

By means of the present method it is possible to position anunlightened, or at least comparatively unlightened, submarine tube, witha resulting economy of positioning costs. Furthermore, the length of thesuccessive tube elements to be positioned is irrelevant, and the methodenables the tube to be constructed on board the positioning craft withthe help of short screwed or welded sections. Since the guide isprovided for a given maximum positioning depth, positioning may beperformed at any intermediate depth without major modification using aguide of simple and inexpensive construction, and the method thus hasgreat flexibility of utilisation.

In addition the positioning speed may easily be adjusted or stopped bymeans of the brake without the use of auxiliary stoppage floats, and thetube need not be subjected to substantial traction forces at thesurface, thus enabling tugs of comparatively low power to be employed.

The rigidity of the guide is added to that of the tube in the upperportion of the S-shaped curve, where the flexural constraints aregreatest when positioning is stopped, and devices may be installed tocheck the shape and location of the upper portion of the S-shaped curve.The guide and tube assembly offers little grip or purchase to marinecurrents, and-in the case of positioning across the current-readilyassumes the form of a skew curve, while in the event of bad weather, itcan be immersed and laid on the sea bed so that it is sheltered frommarine currents and from the surface swell.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent, is:

In a method for laying a hollow steel pipe to be used as a pipeline onan immersed bottom from one shore to another shore by imparting to saidpipe a resilient deformation in an immersed section thereof that joins apipe portion already laid to a pipe portion awaiting to be laid beingsuch that said pipe section has a lower branch tangential to the bottomand an upper branch having a horizontal terminus and an S-curve betweenthe bottom and said horizontal terminus, the S-curve having aninflection point between said branches, said section progressivelysinking to the bottom during laying of the pipe so that the S-curveadvances toward said another shore with said horizontal terminus movingabove and in advance of said inflection point and said inflection pointmoving above and in advance of the point at which said lower branch istangential to the bottom, with said horizontal terminus and saidinflection point and said tangential point all advancing in that orderlengthwise along the pipe, said pipe further having by itself whenimmersed a negative buoyancy; the improvement comprising imparting tosaid upper branch a positive buoyancy by supporting said upper branch onand for sliding movement relative to an elongated guide which extendsfrom adjacent said inflection point to adjacent said horizontal terminusand which is flexible in all transverse directions while applying upwardbuoyant forces to said guide simultaneously at a plurality of pointsdistributed lengthwise of the guide, the sum of said buoyant forcesbeing greater than the sum of the submerged weights of said guide andsaid upper branch, moving said guide relative to said pipe whilemaintaining the positions of said forces fixed relative to each otheralong the length of the guide, in the direction of said another shore,at a speed equal to the speed of v laying said pipe, while exerting onsaid pipe adjacent the with the latter portion adjacent the vicinity ofbut below 5 the surface of the water and in a position substantiallyparallel to the surface of the water, said deformation surface of thewater a horizontal traction in. the direction of said another shore.

References Cited by the Examiner UNITED STATES PATENTS 35,128 4/1862Shaw 61--72.3 1,060,785 5/1913 Pahl 6172.3 1,569,764 1/ 1926 Lock-wood61--72.3 1,703,777 2/ 1929 Pernot 6172.3 X 2,692,092 10/ 1954 Kinsinger6172.6 X 2,783,027 2/ 1957 Gilbert 6172.3 X 2,871,665 2/1959 Brandt61--72.3 2,910,835 11/1959 Timothy 61-723 FOREIGN PATENTS 1,206,378 8/1959 France. 1,230,014 3/ 1960 France.

863,000 3/ 1961 Great Britain. 128,713 7/ 1960 Russia.

OTHER REFERENCES Construction Methods and Equipment, March 1957, pp.156, 157, and 163.

EARL J. WITMER, Primary Examiner. JACOB L. NACKENOFF, Examiner. T. W.FLYNN, Assistant Examiner.

